Recognition pattern of CTL clone RDR2 on MM cells and normal hematopoietic cells. Recognition of MM cells by RDR2 in a heterogeneous bone marrow sample of an mHag-positive patient was determined in CFSE-based cytotoxicity assays after incubation with a control CMV-pp65-A2–specific CTL clone (left dot plot) or with CTL RDR2 (right dot plot) in 1:1 effector-target (E/T) ratios. CFSE-negative cells represent the CTL clones. Strong specific recognition of CFSE-positive CD138 APC-counterstained MM cells was observed (A). Recognition by RDR2 (▪) and control allo-A2 CTL (□) was tested in CFSE-based cytotoxicity assays and by IFN-γ secretion. Heterogeneous cell samples were incubated with CTLs at a 1:1 E/T ratio for 4 hours. Patient bone marrow cells were counterstained with CD138 mAb for detection of MM cells or with CD3 mAb for detection of T cells. Patient-derived MM cells were strongly lysed by RDR2 whereas T cells were weakly recognized. Both EBV-LCLs and PHA blasts were strongly lysed (B). PBMCs from 3 healthy mHag-positive donors were counterstained with different lineage-specific markers. Lysis by RDR2 was significantly diminished in both B cells (P = .02) and T cells (P < .001) as compared with lysis by allo-A2 CTL (shown as mean value ± SD) (C). Stimulation of CTLs was measured by INF-γ release after 24 hours of coculture. RDR2 stimulation by resting PBMC subpopulations was low as compared with allo-A2 CTL stimulation whereas activated B cells (EBV-LCL) induced similar IFN-γ release in both CTLs (D).